(a) Field of the Invention
The present invention relates to a liquid developer for use in electrostatic photography which comprises a toner consisting essentially of a pigment or a dyestuff and a non-aqueous dispersion of a specific polymer, said toner being uniformly dispersed in a carrier liquid having a high insulating property and a low dielectric constant.
(B) Description of the Prior Art
Generally, liquid developers for use in electrostatic photography are prepared by dispersing a toner consisting essentially of carbon black, organic pigment or organic dyestuff and synthetic or natural resin such as acrylic resin, phenol-modified alkyd resin, rosin, synthetic rubber, etc. with the addition of a polarity controlling agent such as lecithin, metallic soap, linseed oil, higher aliphatic carboxylic acid, etc. in a carrier liquid having a high insulating property and a low dielectric constant, such as a petroleum type aliphatic hydrocarbon. Such a toner undergoes electrophoresis in response to the electric charge of an electrostatic latent image formed in the surface layer of an electrophotographic sensitive material or an electrostatic recording material in the course of development, and it fixes on the surface of said latent image and forms a copied image. The conventional liquid developers, however, have been defective in that the resin and/or the polarity controlling agent contained therein diffuse in the carrier liquid to make the polarity indistinct, resulting in an indistinct copied image due to a lowering of the concentration of the image and the fixability, an increase of stained ground, etc. Moreover, the conventional toners, once aggregated, cannot be redispersed, and therefore, reuse thereof has been difficult. Furthermore, because of these defects, the conventional liquid developers have been disqualified for use in offset printing or in transferring process such as charge transfer, pressure transfer, magnetic transfer, etc.